the tyre issue was well known in the past. More than 2 years ago. Search for feathering or cupping on here. Bridgestone went and changed the tyre design and pattern number and Nissan also issued a change to the suspension to prevent this from happening. How old were the tyres. The sound from problem ones would sound more like a wheel bearing going and by feeling the outer tread edge of these tyres you can feel the uneven where on the tread.
Bridgestone tyre code contains KZ (older tread pattern) rather than XZ (newer). Nissan in the past did replace these under warranty in the UK.I had mine done. That was some time ago.
I'm not convinced by the mechanics diagnosis.